It is often desirable to somehow remove and test a tissue sample, particularly in the diagnosis and treatment of cancerous tumors, pre-malignant conditions and other diseases or disorders. Typically, when the physician establishes by means of procedures such as palpation, x-ray or ultrasound imaging that suspicious circumstances exist, it is important to determine the condition of the cells (e.g. whether the cells are benign or cancerous by performing a tissue biopsy). Biopsy may be done by an open or closed technique. Open biopsy removes the entire mass (excision biopsy) or a part of the mass (incision biopsy). Closed biopsy, on the other hand, is usually done with a needle-like instrument and may be either an aspiration or a core biopsy. In needle aspiration biopsy, individual cells or clusters of cells are obtained for cytologic examination and may be prepared such as in a Papanicolaou smear. In core biopsy, as the term suggests, a core or fragment of tissue is obtained for histologic examination.
The type of biopsy depends in large part on circumstances present with respect to the patient and no single procedure is ideal for all cases. However, core biopsy is extremely useful in a number of conditions and is being used more frequently by the medical profession.
A variety of biopsy instruments and devices have been described and used for obtaining specimens of tissue. For example, reference is made to U.S. Pat. Nos. 4,651,752; 4,702,260; and 4,243,048 which show biopsy instruments of varying types. Additionally, a number of very specialized devices for extracting samples of tissue have been described such as the biopsy device in U.S. Pat. No. 4,461,305, for removing a sample of tissue from the female uterine cervix.
Other devices have been disclosed which relate to surgical cutting instruments. For example, U.S. Pat. No. 4,589,414 discloses an instrument which is particularly designed to operate in the area of the knee to withdraw tissue chips. Also available are so-called biopsy guns for removing a core of tissue. Such guns customarily are spring powered devices and must be cocked with considerable force. When actuated, such guns produce a loud snapping noise, combined with a jerking action. Such a biopsy gun may employ a needle set consisting of an inner stylet and an outer tube called a cannula. The stylet is a needle like device with a notched cut-out at its distal end. The cannula in effect is a hollow needle with an angled cutting surface at its distal end which slides over the stylet. When the stylet is forced into tissue, the tissue is pierced and relaxes into the notched cutout of the stylet. When the cannula is then slid forward, the tissue in the notch of the stylet is sliced off and retained in the notch until the cannula is withdrawn. Examples of such gun devices are shown in U.S. Pat. Nos. 4,600,014 and 4,699,154.
Although such spring powered biopsy guns will remove a core or sample of the tissue, they have rather serious disadvantages. For one, they must be manually cocked with a plunger bar. Such "cocking" of the gun requires considerable force and the gun must be cocked for each biopsy cut. A further disadvantage is that the springs provided in the gun accelerate the needles until a mechanical stop position is reached, creating a loud snapping noise and jerking motion which is a problem both to the physician and the patient. This noise and jerking action can cause the patient to jump and in some cases may prevent the physician from striking the intended tissue target. Another disadvantage is that the force and velocity delivered to the stylet and cannula rapidly diminishes when traveling from a retracted to a fully extended position resulting in tissue samples of lower quality. Furthermore, once the biopsy gun is released, the physician has no control over the instruments function until the biopsy is completed and cannot continue to guide the instrument by feel.